JPH07289566A - Titanium orthodontic parts - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a safe titanium orthodontic component with excellent mechanical properties. [Structure] (1) Mixing titanium raw material powder and binder to obtain a mixture (2) Molding the mixture by injection molding to obtain a molded body (3) Removing binder in the molded body and (4) A titanium orthodontic component manufactured through a step of sintering a molded body from which a binder has been removed to obtain a sintered body, wherein the obtained sintered body has carbon: 0.25 wt% or less, oxygen: 0.
It has a composition containing 6 wt% or less and the balance Ti and unavoidable impurities, and has a relative density of 97.0% or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium-based orthodontic part manufactured by a metal powder injection molding method.

[0002]

2. Description of the Related Art Conventional orthodontic parts are made of metal, ceramic or polymer resin.
Since the color tone of ceramics or polymer resins is close to that of living teeth, it is more aesthetic than metal. Some ceramics are manufactured by powder injection molding. Stainless steel is generally used because of its corrosion resistance and is widely used because of its excellent mechanical properties. Those made of metal are manufactured by metal powder injection molding or cutting.

However, these orthodontic components have the following problems. That is, the ceramic and polymer resin products are inferior in mechanical properties to those made of stainless steel, and there is a risk of damage during use or damage to the oral cavity. Further, stainless steel has problems such as carcinogenicity and allergies due to the influence of contained elements such as Ni (for example, “dental metal material”, special steel, 42).
Vol. 11, No. 11, P42).

Although Ti is known to be excellent as a metal for biomaterials, it has poor machinability and it has been difficult to manufacture an orthodontic component having a minute complicated shape by machining. Further, a method for producing a titanium part by a metal powder injection molding method is disclosed in Japanese Patent Application Laid-Open No. 2-54733, etc., but in order to obtain required characteristics due to the characteristics of an orthodontic part having a small shape and a complicated shape. Was not enough.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems and utilizes a metal powder injection molding method, and is a safe titanium orthodontic part having excellent mechanical properties. The purpose is to provide.

[0006]

As a result of various studies, the present invention provides a method for solving the above-mentioned problems. That is, the present invention includes (1) a step of mixing a titanium raw material powder and a binder to obtain a mixture, (2) a step of molding the mixture by injection molding to obtain a molded body, (3) a step of removing the binder in the molded body, and (4) A titanium orthodontic component manufactured through a step of sintering a molded body from which a binder has been removed to obtain a sintered body, and the obtained sintered body has a carbon content of 0.25 wt% or less. , Oxygen: 0.
The present invention provides a titanium orthodontic part having a composition of 6 wt% or less, a balance of Ti and unavoidable impurities, and a relative density of 97.0% or more.

The obtained sintered body has a hardness of H _RV 100 to 3
20 and the elongation is preferably 2% or more.

The surface of the compact after sintering is oxidized or nitrided,
Alternatively, it is convenient that a coating treatment with gold or a gold alloy has been subjected to a modification treatment such as increasing the hardness and / or changing the surface color.

The titanium raw material powder used has an average particle size of 25.
μm or less, carbon content of 0.25 wt% or less, oxygen content of 0.
It is preferably 6 wt% or less.

The step of removing the binder is preferably carried out in an inert atmosphere or under reduced pressure.

The step of sintering the molded body from which the binder has been removed is preferably carried out in a vacuum or in an inert atmosphere in the presence of a getter material. Furthermore, it is preferable that the degreased molded body be placed in another container in a sintering furnace and sintered.

[0012]

The titanium orthodontic part of the present invention is manufactured by utilizing the metal powder injection molding method, and is manufactured through the following steps. (1) Mixing titanium raw material powder and binder to obtain a mixture (2) Molding the mixture by injection molding to obtain a molded body (3) Removing binder in the molded body and (4) Removing binder Of sintering the formed compact to obtain a sintered compact

According to the present invention, it has become clear that the mechanical properties of the sintered body, that is, the orthodontic part, in particular the tensile strength and elongation, are determined by the carbon and oxygen contents and the relative density of the sintered body. In other words, in order to obtain orthodontic components that are titanium-based with low risk of carcinogenicity and allergies and satisfy the required mechanical properties at a general price, the carbon content and oxygen content should be minimized and sufficient. It is necessary to obtain a sintered body of various densities. When carbon and oxygen penetrate into titanium, stable oxides or carbides are formed and are difficult to remove, and the material becomes brittle, so that the elongation is reduced and the tensile strength is also generally lowered. Further, the strength and hardness of the sintered body are greatly affected by the density, and the mechanical characteristics are deteriorated due to the decrease in the density. Further, the impact resistance is significantly affected by the density, and at a density of 95% or less, the impact resistance is reduced to about 1/10 of that of a non-void material having the same material composition.

In order to obtain a titanium orthodontic part having sufficient mechanical properties, which is the object of the present invention, the carbon content, oxygen content and relative density of the orthodontic part, that is, the sintered body, are determined for the above reasons. It is limited to the following range. The reason will be described below.

First, regarding the carbon content, as is known in the melting material, the toughness is remarkably lowered with an increase of about 0.4%, and the carbon content is 0 due to the influence of the oxygen content and the density. When it exceeds 0.25 wt%, it is difficult to secure an elongation of 2% or more, preferably 3% or more, which is considered necessary for an orthodontic component even with a low oxygen content and high density sintered body. Therefore, the carbon content range of the orthodontic component of the present invention is set to 0.25 wt% or less.
It is preferably 0.15 wt% or less.

Similarly, the oxygen content is also examined, and the maximum oxygen content allowable for ensuring the above elongation is 0.6 wt%. Therefore, the range of the oxygen content of the orthodontic part of the present invention is set to 0. It should be less than 6 wt%. It is preferably 0.5 wt% or less.

The density of the sintered body has a great influence on its mechanical properties, and a material without voids is most preferable, but the conditions required for densification are complicated, and it is economical to obtain a material without voids. And it is often difficult in the manufacturing process. Therefore, as a result of diligent examination of the density required to obtain an orthodontic part having excellent mechanical properties, which is the object of the present invention, it is necessary to obtain a density of 97% or more if the carbon and oxygen contents are satisfied. It has become clear that it satisfies various mechanical properties.
Therefore, the relative density of the orthodontic component of the present invention is set to 97% or more.

The sintered body is used as an orthodontic part after post-treatment such as surface polishing and shape correction. This orthodontic part is made of Ni,
It does not contain elements that cause allergies to the human body, such as Cr, and has higher mechanical properties than those made of ceramics or polymer resins. However, to such Warekake it does not occur, 2% or more preferably requires elongation of at least 3%, also the hardness (H _RV) seems to require from 100 to 320. This is because it is desirable to avoid cracks and deformations because damage to the inside of the mouth due to cracks or deformations when a strong force is applied to the parts due to contact with food during use.

The present invention defines the carbon content, oxygen content and relative density ranges of orthodontic parts and utilizes metal powder injection molding to achieve these. This method can be realized by combining raw materials and conditions of each step. In the present invention, it is carried out according to the following preferable conditions in each step. (1) Mixing titanium raw material powder and binder to obtain a mixture (2) Molding the mixture by injection molding to obtain a molded body (3) Removing binder in the molded body and (4) Removing binder Of sintering the formed compact to obtain a sintered compact

The production method of the titanium raw material powder used in the present invention is not particularly limited, but in order to obtain the purity desired in the present invention, the purity and specific surface area of the titanium raw material powder,
The particle size is set as follows.

That is, the purity of the titanium raw material powder is an important characteristic directly related to the purity of the product after sintering. Therefore, the carbon content and the oxygen content of the raw material powder are 0.25% or less and 0.6% or less, preferably 0.1% or less and 0.3% or less, respectively, and the purity excluding these elements is set. Is preferably 99.5% or more. Further, since the oxygen content of the raw material powder tends to depend on the specific surface area of the powder, the specific surface area of the powder satisfying the above oxygen content is generally 0.15 m ² / g or less.

The characteristics of these raw material powders are generally easier to obtain as the particle size of the powder is coarser. However, even if the purity is satisfied, it is difficult to obtain the orthodontic component intended by the present invention unless the relative density is 97% or more. In order to obtain high density, it is preferable that the particle size of the powder is fine. Also, in order to obtain a minute shape of the orthodontic part, especially a sufficient strength of the part to be bonded to the tooth, the fine structure of the contact part is important,
The presence of coarse particles is not preferable for realizing the present invention in order to obtain this at the time of molding. Therefore, the particle size (average particle size) of the powder used in the present invention is preferably 25 μm or less.

As for the binder used in the present invention, it is preferable to use a binder having a lower oxygen content, because it is easier to prevent migration of oxygen to the titanium powder during debinding, but it is possible to prevent an increase in powder oxygen content depending on the debinding conditions. Since it can be suppressed, the type of binder used in the present invention is not particularly specified. Typically EVA, PP, PE, P
Resins such as BMA are listed, and these are WAX,
A plasticizer or the like can be included.

First, the titanium raw material powder and the binder are mixed. In this step, a kneader such as a general kneader or a general heating mixer can be used. The selection of the mixer can be arbitrarily selected according to the powder to be used and the characteristics of the binder, and is not particularly specified in the present invention, but in order to obtain a good product it is sufficient to wet the raw material powder and the binder. preferable. For this purpose, it is important to apply a sufficient shearing force to the mixture at the time of kneading and to mix the binder so as to improve the wettability with the surface of the metal powder.

Next, the mixture of the titanium raw material powder and the binder thus obtained is injection molded by an injection molding machine. In this molding step, since the physical properties of the mixture change depending on the physical properties and the mixing ratio of the titanium raw material powder and the binder, it is necessary to perform the molding with a molding machine and molding conditions according to the physical properties. Not specified.

Generally, a mold used for molding is similar to a plastic molding mold, but the orthodontic component of the present invention has a fine and complicated shape, and therefore, such a fine complicated structure in general plastic molding is used. It is preferable to apply a molding technique for parts, and similarly for a mold, a mechanism for smoothly operating a large number of slides is required. Also,
It is desirable that the shape of the back surface of the bonding portion should be a shape including a part of a cylinder or a sphere, in order to allow smooth operation of a large number of minute parts and to enable sufficient bonding with teeth.

The structure of the molding die of the present invention is not particularly limited as long as the target shape can be obtained, but in order to satisfy the economical efficiency and the sufficient adhesion to the teeth, a gate width of 1 mm is used using a hot runner or the like. The following is desirable.

Next, the binder is removed from the obtained molded body. This step is not particularly limited as it depends on the selection of the binder. However, in general, it is necessary to quickly remove the binder so that the carbon contained in the binder does not stay in the titanium powder forming the molded body or the floor plate of the molded body. Therefore, it can be said that it is desirable to remove at a relatively low temperature (for example, 100 to 350 ° C.).

In order to accelerate degreasing, treatment under reduced pressure or in an inert atmosphere is effective from the viewpoint of suppressing the increase in oxygen and carbon contents. Furthermore, it is also effective to place in a reactive atmosphere and environment that accelerates the decomposition of the polymer resin constituting the binder in a relatively low temperature range where the transfer of oxygen and carbon of the powder is difficult to proceed.

Finally, the molded body from which the binder has been removed is sintered. A major problem in this process is how to suppress the increase of powder having a high surface area and a high affinity with oxygen. In particular, an orthodontic component has a fine and complicated shape and therefore has a large surface area relative to its weight, and carbon, oxygen, and the like are easily infiltrated, and sufficient characteristics cannot be obtained by a known sintering method.
As a result of intensive studies by the inventors on this problem, basically, the oxygen content of the sintered body after sintering is determined by whether or not the oxygen potential of the environment in which the molded body after debinding is set can be kept low as follows. It was concluded that it would be done. In order to keep the oxygen potential at the time of this sintering low, the furnace structure,
It was clarified that the atmosphere, the material of the floorboard, etc. had a great influence, and the desirable conditions for realizing the present invention were obtained.

The heating system and atmosphere of the sintering furnace used in the present invention are not particularly limited. However, in order to suppress an increase in oxygen in the debindered (degreased) molded body, it is desirable that the structure be capable of sintering in a vacuum or in an inert gas atmosphere, so that oxygen and carbon from the vicinity of the molded body can be prevented. In order to suppress these, it is desirable to provide a container (preferably made of graphite) inside the furnace container for these molded products, insert a degreased molded product into the container, and perform the sintering treatment. In addition, it is desirable to install a substance capable of absorbing oxygen and carbon as a getter in the vicinity of the molded body in this container. The amount and material of the getter are selected depending on the positional relationship with the molded product, the material of the floor plate, and the shape of the container.However, according to the study by the inventors, the use of titanium scrap as the getter enables economical and effective suppression of impurity intrusion. It was

If necessary, the obtained sintered body is used after finishing such as polishing the surface or modifying the shape. The polished metal product is glossy and has aesthetics such as ceramics or polymer resin. Since it is inferior to manufactured products, it is possible to modify the surface by heat treatment or coating such as plating to change it to a state close to the color tone of teeth before use.

To modify these surfaces, it is possible to add a method such as nitriding or oxidation by CVD or plating with gold or a gold alloy. It is necessary to select a method that can satisfy the object of the present invention because the aesthetics can be improved by these techniques but the surface of the orthodontic component has a property different from that of pure titanium so that biocompatibility is deteriorated.

Further, it is possible to obtain the effect of improving the surface hardness by coating, and the sliding property with the wire during orthodontic treatment can be improved.

[0035]

EXAMPLES The present invention will be described in more detail based on the following examples.
To explain. (Example 1) Gas pure titanium powder shown in Table 1 was used as the raw material.
It was a fee. Carbon and oxygen contents were determined by combustion analysis.
The average particle size is measured by a laser diffraction type particle size distribution measuring device.
The specific surface area was measured by the BET method.
About 30% by volume of thermoplastic resin (Mitsubishi Chemical
SB 125, 50% made by Seisha, wax, (wax made in Japan
WAX130, 40%) plasticizer (manufactured by Shin Nippon Rika Co., Ltd.
Butyl phthalate, 10%) organic binder
Add and knead for 30 minutes at 130 ℃ with a pressure kneader.
It was given and the compound was created. The obtained compound
The viscosity of is measured with a capillary-type viscosity measuring device.
As a result, the shear rate was 1216 at 150 ° C. ^-1Viscosity is 1
It was 100 Poise. With this compound,
Orthodontic section using an online screw type injection molding machine
The product was molded. In parallel, pulling for mechanical property measurement
A test piece was molded. Specifically, it is as follows.

(Molding conditions) The molding conditions were all the same as condition A in the table. However, since the viscosity of the raw material compound differs depending on the raw material powder, only the injection pressure and the holding pressure during molding were changed and modified. Molding temperature 140 ℃ Mold temperature 2
The temperature was 5 ° C.

The obtained molded body was subjected to a reduced pressure atmosphere (10 to 10
^-5 Torr) and after heating to 200 ° C. in an argon gas stream, the temperature was raised to a maximum temperature of 280 to 450 ° C. in 12 hours to specifically remove the binder under the following conditions.

(Degreasing Conditions) For degreasing, it is necessary to prevent oxidation of titanium powder from the atmosphere, prevent carbon and oxygen from entering due to decomposition of the binder, and reduce gas generation in the sintering furnace. is there. The maximum temperature is 300 ° C under degreasing condition A, and 350 ° C under B
And C was set to 450 ° C. These conditions and atmosphere,
The properties of the degreased body are determined by a combination of conditions such as the temperature rising rate and the binder type.

The debindered compact was placed on a zirconia base plate with a smooth surface in a sintering furnace, and the temperature was raised to 800 ° C. at a vacuum degree of 1 Toor or more under the following conditions, and then 1200 ° C. in argon gas. Sintering was performed by holding at 2 ° C for 2 hours.

(Sintering conditions) In condition A, the amount of Ti scrap getter charged was twice as much as the weight of the product in the vicinity of the molded body and then charged in a graphite box. In condition B, the getter was set to ½ of the product weight, and the same box as above was used. Condition C was performed under the condition that neither getter nor box was used.

The hardness of the obtained sintered parts and the sintered test pieces was measured, and the mechanical properties were confirmed by the test pieces.

As a result, the oxygen content, carbon content and hardness of the part and the test piece were similar and consistent. Therefore, it was determined that mechanical properties equivalent to those of the test piece could be obtained. Table 1 shows the chemical composition, density, and mechanical properties of the obtained sintered body. The strength and elongation were measured using a dumbbell-shaped test piece with an autograph type tensile tester. The hardness was measured by a micro Vickers hardness meter.

Example 2 Table 2 shows a comparison with the conventional method. It is apparent that the characteristics of the orthodontic component of the present invention are excellent methods satisfying mechanical characteristics and biocompatibility as compared with conventional ones. Compared with the ceramics and stainless steel parts of Comparative Examples 1 and 2, the aesthetics may be slightly inferior, but there is little risk of damage in the oral cavity due to their excellent mechanical properties. However, it is possible to avoid the carcinogenicity and allergenicity caused by the inclusion of Ni and the like in stainless steel parts. Further, in the conventional attempts to apply titanium to orthodontic parts, it has been difficult to industrially manufacture the removal process due to the poor machinability of titanium and the minute and complicated shape of the parts.
Similarly, in the production by metal powder injection molding, it was difficult to achieve practical use because the mechanical properties equivalent to those of the ingot material could not be achieved.

Table 2 shows the conventional manufacturing method again. These 1 to 4 show the characteristics of general products manufactured by each company.

The commercially available polymer resins and ceramics of Comparative Examples 1 and 4 are inferior to the examples of the present invention in that there is almost no elongation and that the parts may crack and damage the mouthpiece.

The stainless steel parts of Comparative Examples 2 and 3 have substantially the same elements even if they are processed differently.
A material containing Ni and Cr is generally used to obtain corrosion resistance,
Although it has excellent mechanical properties, it may cause allergies.

It can be said that titanium is the most desirable material for achieving both mechanical properties and avoidance of allergies. However, as shown in Comparative Example 5, since the shape of the parts is complicated and small, it is difficult to manufacture at a unit price that is generally usable when manufactured by cutting. Comparative Example 6 shows a conventional MI
As shown in the comparative example of Table 1, the characteristics of the titanium parts manufactured by M are as follows.
It was difficult to use because of poor mechanical properties.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

EFFECTS OF THE INVENTION The titanium orthodontic component of the present invention has a certain composition and density by utilizing the metal powder injection molding method, and therefore has better mechanical properties, biocompatibility, and aesthetics than conventional ones. It is excellent and can be used without worrying about allergies or carcinogenesis.

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Claims (7)

[Claims] 1. A step of (1) mixing titanium raw material powder and a binder to obtain a mixture (2) a step of molding the mixture by injection molding to obtain a molded body (3) a step of removing the binder in the molded body, and ( 4) A titanium orthodontic component manufactured through a step of sintering a molded body from which a binder has been removed to obtain a sintered body, and the obtained sintered body has a carbon content of 0.25 wt% or less, Oxygen: 0.
An orthodontic part made of titanium, containing 6 wt% or less, having a composition of the balance Ti and unavoidable impurities, and having a relative density of 97.0% or more. 2. The obtained sintered body has a hardness of H _RV 100-3.
20. The titanium orthodontic part according to claim 1, having an elongation of 20% or more. 3. The titanium orthodontic component according to claim 1, wherein the surface of the molded body after sintering is modified. 4. The titanium raw material powder used has an average particle size of 25.
The titanium orthodontic part according to any one of claims 1 to 3, which has a micrometer or less, a carbon content of 0.25 wt% or less, and an oxygen content of 0.6 wt% or less. 5. The titanium orthodontic component and the method for producing the same according to claim 1, wherein the step of removing the binder is performed in an inert atmosphere or under reduced pressure. 6. The step of sintering the molded body from which the binder has been removed is carried out at a temperature of 100 to 350 ° C. under vacuum or in an inert atmosphere in the presence of a getter material. Orthodontic parts made of titanium according to. 7. The orthodontic part made of titanium according to claim 6, wherein the step of sintering the molded body from which the binder has been removed is carried out by placing the molded body in another container in a sintering furnace.